1. Field of the Invention
The invention relates generally to a press having a hydraulically controlled platen. More particularly, the press is useful for the manufacture of prefabricated building components (such as trusses) or other building components. It may also be useful in processing other articles (such as plastic sheet, plastic pipe, sheet and metal articles such as aluminum extrusions, laminated and composite timber articles).
2. Description of the Related Art
Whilst the following discussion illustrates the press used for manufacture of prefabricated building components, it is to be understood that the press may be used in other engineering applications.
Traditionally, trusses that are destined for the building industry may be constructed on-site or prefabricated. Prefabricated trusses of standard designs are very popular as they can be mass-produced by passing the assembled components between a press which fixes the components together at appropriate locations.
Typically, such presses have an upper and/or lower platen against which the fixing occurs. One form of press, which is in use in the building component prefabrication industry, has a lower platen and an upper moving platen which is designed to press down on the components disposed in between them. The pressing action pushes fasteners into the components to form timber joints of a truss assembly. The components need to be held firmly during the fixing operation to produce strong and uniform trusses. Considerable pressure is applied to the lower platen indirectly during the holding and fixing of the timber joint to achieve this. Further, the fixing is usually localized to relatively small areas of the platen where the joint to be formed is located. This area may vary across the platen depending upon where the proposed joint is positioned.
Consequently, the lower platen has to be supported by devices which prevent it moving or tilting in response to any localized pressure applied to it. A number of these types of devices have been proposed.
In Australian patent no. 543663 a hydraulic press is disclosed. A pair of rams are each provided with a hydraulic device under the tool. They are connected by a torsion bar which regulates the fluid flow into the hydraulic rams in the event that it becomes misaligned. A complex combination of bars, rocking members and springs are used to maintain the tool level.
In another arrangement, a series of manually or automatically controlled levers are provided to mechanically regulate the movement and alignment of the platen of a press. Again, this is complex and is not readily adapted to automate and regulate the pressing function of the machine.
It is an objective of the present invention to provide a press with improved adjustment of the alignment of at least one of its pressing components.
Accordingly there is provided a press for fabrication of building components including: (a) an upper platen; (b) a lower platen; (c) first and second hydraulic devices each including; (i) a cylinder; (ii) a piston located in the cylinder defining a first and a second chamber in the cylinder, the piston sealingly engaging the cylinder and movable in the cylinder; and (iii) a piston rod connected to the piston and extending through the second chamber, wherein the first and second chambers, each have an inlet/outlet for hydraulic fluid and the second chamber of the first hydraulic device is in fluid communication with the first chamber of the second hydraulic device; and each piston rod of each hydraulic device extends in engagement with one and the same of the upper or lower platens, whereby the hydraulic devices are operable to shift the upper or lower platen the piston rods engage, relatively toward or away from the other of the upper or lower platens, (d) a pump to pump hydraulic fluid into the first chamber of the first hydraulic device; and (e) a valve in fluid communication with the first chambers of the first and second hydraulic devices to selectively withdraw hydraulic fluid from the first chamber of either or both the first and second hydraulic devices to align the upper and lower platens.
In operation, hydraulic fluid is pumped into the first chamber of the first hydraulic device by the pump which causes the piston to move towards the inlet/outlet of the second chamber. The second chamber decreases in volume and forces hydraulic fluid through the inlet/outlet of the second chamber of the first hydraulic device into the first chamber of the second hydraulic device. This in turn, causes a similar displacement of the piston in the second hydraulic device and fluid present in the second chamber of the second hydraulic device flows through the inlet/outlet.
As will be well understood by engineers, hydraulic fluid is substantially incompressible and is a medium which can translate motive forces very well.
In another preferred form of the invention there is provided, a press for fabrication of building components including: (a) an upper platen connected to an upper part of a frame; (b) a lower platen; (c) spaced first and second hydraulic devices each connected at one and the same end thereof to the frame and each including; (i) a cylinder; (ii) a piston located in the cylinder defining a first and a second chamber in the cylinder, the piston sealingly engaging the cylinder and movable in the cylinder; and (iii) a piston rod connected to the piston at one end thereof and extending through the second chamber into engagement with the lower platen at the other end of the device to that connected to the frame; wherein the first and second chambers, each have an inlet/outlet for hydraulic fluid, and the second chamber of the first hydraulic device is in fluid communication with the first chamber of the second hydraulic device; (d) a pump to pump hydraulic fluid into or from the first chamber of the first hydraulic device to cause the piston rods of both hydraulic devices to move and to shift the upper or lower platen relatively towards or away from the other platen; and (e) a valve in fluid communication with the first chambers of the first and second hydraulic devices to selectively withdraw hydraulic fluid from the first chamber of either or both the first and second hydraulic devices to align the upper and lower platens.
In yet another preferred form of the invention there is provided, a press for fabrication of building components including: (a) an upper platen connected to an upper frame; (b) a lower platen connected to a lower frame; (c) spaced first and second hydraulic devices, each including; (i) a cylinder; (ii) a piston located in the cylinder defining a first and a second chamber in the cylinder, the piston sealingly engaging the cylinder and movable in the cylinder; and (iii) a piston rod connected to the piston at one end thereof and extending through the second chamber; wherein the first and second chambers, each have an inlet/outlet for hydraulic fluid, and the second chamber of the first hydraulic device is in fluid communication with the first chamber of the second hydraulic device; and each of the hydraulic devices is connected at one end to the upper frame and at the other end to the lower frame, one of the connections being with the end of the piston rods extending from the second chambers, and the devices being operable by extension or retraction of the piston rods thereof to shift the upper or lower platen relatively toward or away from the other; (d) a pump to pump hydraulic fluid into or from the first chamber of the first hydraulic devices to cause the piston rods of both hydraulic devices to move and to shift the upper or lower platen relatively towards or away from the other platen; and (e) a valve in fluid communication with the first chambers of the first and second hydraulic devices to selectively withdraw hydraulic fluid from the first chamber of either or both the first and second hydraulic devices to align the upper and lower platens.
According to another preferred form of the invention, a press for fabrication of building components is provided including: (a) an upper platen; and (b) a lower platen; (c) first and second hydraulic devices each including; (i) a cylinder having a partition sealingly engaging the walls of the cylinder and located intermediate the ends of the cylinder, to define first and second chambers of the cylinder; (ii) a first piston located in the first chamber and defining (a) a first sub-chamber between an end of the cylinder and the first piston and (b) a second sub-chamber between the first piston and the partition, the first piston sealingly engaging the cylinder and movable in the cylinder; (iii) a second piston located in the second chamber and defining (c) a third sub-chamber between the partition and the second piston and (d) a fourth sub-chamber between the second piston and the other end of the cylinder, the second piston sealingly engaging the cylinder and movable in the cylinder; and (iv) a piston rod connected to the first piston and the second piston and passing through and sealingly contacting the partition; and further extending from the fourth sub-chamber; wherein the first sub-chamber has an inlet for hydraulic fluid, the second sub-chamber has an outlet for hydraulic fluid, the third sub-chamber has an inlet/outlet for hydraulic fluid and the fourth sub-chamber has an inlet/outlet for hydraulic fluid; and the inlet/outlet of the third sub-chamber of one of the hydraulic devices is in fluid communication with the inlet/outlet of the fourth sub-chamber of the other hydraulic device; and each of the hydraulic devices is connected at one end to the upper frame and at the other end to the lower frame, one of the connections being with the end of the piston rods extending from the fourth sub-chamber and each device is operable by extension or retraction of the piston rods thereof to shift the upper or lower platens relatively toward or away from the other; (d) a pump to pump hydraulic fluid into the first sub-chamber of each of the hydraulic devices; and (e) a valve in fluid communication with the first sub-chambers of the first and second hydraulic devices to selectively withdraw hydraulic fluid from the first sub-chamber of either or both the first and second hydraulic devices to align the upper and lower platens.
In operation, hydraulic fluid flows into the sub-chamber of each of the hydraulic devices to apply a load. Typically the load applied to each hydraulic device is different. The pressure applied causes the first and second piston to move which reduces the volume of the fourth sub-chamber of each hydraulic device.
When the load is different on each hydraulic device, the fluid from the fourth sub-chamber which is under the greater pressure, forces fluid into the third sub-chamber of the other hydraulic device. This transmits an additional force to the second piston of that other hydraulic device until its fourth sub-chamber has an equal pressure to the fourth sub-chamber of the first hydraulic device.
In this way, the press reacts quickly to equalize the pressure being applied to the platen which minimizes potential misalignment of the platen.
The press according to the invention, uses the interaction of the hydraulic fluid in the cylinders as the means to maintain the platen substantially level (horizontal) irrespective of the localization of the load imposed by the tool on the platen. Accordingly, the formation of building components, between the upper platen and lower platen over extended periods of use and repetition, is consistently of a high reproducible quality.
Over time, the seals which form the sealing engagement of the piston with the cylinder will degrade and fluid will leak between the chambers in each hydraulic device. As this occurs, the total volume of fluid which resides in the chambers will change. This results in the platen becoming tilted.
Accordingly, to ameliorate this the valve is incorporated to correct any imbalance between the relative position of the pistons in the cylinders.
Preferably, the valve is located in either or both the pistons and is pressure actuated. In this embodiment, the pistons are preferably provided with a passageway which communicates between the chambers of the cylinder. The valve is located in the passageway and under predetermined pressure conditions permits hydraulic fluid to pass from one chamber to another.
In an alternate embodiment, the valve is located externally of the cylinders in a hydraulic fluid line which communicates with a reservoir of hydraulic fluid. The fluid line is connected to each of the cylinders. If the fluid pressure exceeds the predetermined amount in a cylinder, the valve opens to permit hydraulic fluid to flow out and correct any imbalance between the relative positions of the pistons in the cylinders.
In another alternate embodiment, the valve is externally of the cylinders in hydraulic fluid lines which communicate between the hydraulic devices.
In another alternate embodiment, the valve may be actuated in response to sensor signals. Sensors (e.g. electrical limit switches) are positioned to detect the position or alignment of the platen. If predetermined limits are exceeded, the sensors cause the valve or valves associated with either or both the cylinders to open. The pistons are therefore rebalanced to restore the desired alignment.